Most or all computers do something like that. Mine is the Cateye Enduro (or Mightly – same model), and it doesn't display speed below 3-4 km/h. Even when riding at 5 km/h, I think the wheel doesn't spin fast enough for the computer because displayed speed varies endlessly between 4.5 and 5.5 km/h.

My computer still computes the total distance, however, but it's a wired unit.

Regards,